366 D. DAVIDSON BLACK 



the condition of cellular activity may be in other areas of the cor- 

 tex, this portion certainly shows evidence of hyperplasia. This 

 hyperplasia is associated with diminished specialisation of ele- 

 ments as one might expect, yet it is significant to note that the 

 increase in cell content has been conducted in an orderly fashion 

 resulting in a special type of lamination characteristic of this 

 case. 



Trophic activities of afferent fibers 



Roux has pointed out (5) that the development of an active 

 tissue (that is, muscular, nervous or glandular) may be divided 

 into two phases, one which he terms ' self differentiation' in which 

 development goes on without regard to any functional connec- 

 tions, and a second stage termed 'dependent differentiation' 

 where further normal development is not possible unless the tissue 

 functionates. 



Bechterew (1) has shown that the trophic activity of nervous 

 tissue upon nervous tissue, if the supply of nutritive material 

 continue to be normal, depends upon the functional continuity 

 of the neurone systems. 



Thus in cortical development, normal differentiation and evo- 

 lution will cease after the period of ' self differentiation' has passed 

 unless there is functional connection established with lower nerv- 

 ous centers. The end of this period of 'self differentiation' in 

 cortical development is marked in all probability by the first 

 entrance of afferent projection fibers. Full development is 

 reached, as v. Bechterew points out, only when the reflex arc is 

 completed, that is when the efferent projection fiber has estab- 

 lished its peripheral connections. These generalities of course 

 apply only to projection centers, but as association areas are pri- 

 marily dependent upon projection centers in their development, 

 it is not necessary to consider them in this connection. 



There is thus a critical point, as it were, beyond which, in the 

 absence of functional connections, any attempts towards differen- 

 tiation will take place along quite unusual lines. 



In this case afferent projection fibers reached certain areas of 

 the cortex in an abnormal way and came in contact with neurones 

 in the outer cell strata. The effect of this contact was to start 



